The invasive weed Centaurea maculosa (spotted knapweed) has become widespread in North America. Gall flies (Urophora spp.) have been introduced in an attempt at biological control of the plant. The gall flies lay their eggs in the flower heads, where the larvae induce the formation of galls in which they overwinter. The presence of the galls ultimately results in the plants producing fewer seeds. Although the flies have successfully dispersed throughout populations of the invasive weed, they have not proved to be effective control agents, and the weed continues to spread, particularly in areas disturbed by human activity.
Pearson and Callaway have discovered that therein lies a deeper threat. The fly grubs have proved to be an attractive food source for Peromyscus (deer) mice and bolster mouse populations during otherwise lean winter months. This genus of mice are reservoir hosts for the human pathogenic hantavirus, Sin Nombre, and, worryingly, the authors found that the abundance of hantavirus-seropositive mice is elevated in zones of high abundance of weed and flies. Deer mice also act as reservoir hosts for Lyme disease and potentially for plague and other zoonotic pathogens. -- CA
Ecol. Lett. 10.1111/j.1461-0248.2006.00896.x (2006).
